Abstract

The interaction of electrical fields and liquids can lead to a phenomenon that defies intuition. Some famous examples can be found in electrohydrodynamics as Taylor cones, whipping jets, or noncoalescing drops. A less famous example is the floating water bridge: a slender thread of water held between two glass beakers in which a high voltage difference is applied. Surprisingly, the water bridge defies gravity even when the beakers are separated at distances up to 2 cm. In this paper, experimental measurements and simple models are proposed and discussed for the stability of the bridge and the source of the flow, revealing an important role of polarization forces on the stability of the water bridge. On the other hand, the observed flow can only be explained due to the non-negligible free charge present in the surface. In this sense, the floating water bridge can be considered as an extreme case of a leaky dielectric liquid [J. R. Melcher and G. I. Taylor, Annu. Rev. Fluid Mech.1, 111 (1969)].

Received 22 July 2010Accepted 20 October 2010Published online 15 December 2010

Acknowledgments:

The authors thank Dr. Elmar Fuchs for making them aware of the phenomenon of the floating water bridge. Álvaro G. Marín thanks especially Dr. Pablo García-Sánchez for long discussions on the subject and also Professor Antonio Ramos for his useful comments. Álvaro G. Marín dedicates this paper to the memory of Professor Antonio Barrero Ripoll.